The present invention relates to a pretensioner device for automatically increasing the tension of an automotive seat belt.
An automotive seat belt is typically equipped with a seat belt for restraining the vehicle occupant with the aim of preventing the occupant from being thrown forward in case of a vehicle crash or the like. Oftentimes, the seat belt is provided with an emergency locking retractor (ELR) device for locking the winding shaft for the seat belt only in case of an abrupt stop or a vehicle crash without excessively restraining the vehicle occupant in normal situations. Such an ELR device is required to be capable of detecting a deceleration exceeding a prescribed level, and locking up the winding shaft in an extremely short time to prevent the seat belt from being paid out any further.
Simply locking up the winding shaft cannot prevent the seat belt from being paid out by an amount created by tightening the seat belt wound on the winding shaft. In view of this problem, proposals have been made (for instance, in the U.S. Pat. No. 4,705,296) to provide a pretensioner device which can increase the restraining capability of the seat belt by rapidly pulling the buckle which is attached to the seat belt in the direction to increase the tension of the seat belt. Also, to prevent the buckle which has been pulled in this manner from being pulled back by the tension of the seat belt, it has been proposed to provide a means for preventing such a reversing movement, such as a ratchet device or one-way clutch, in addition to the ELR device.
A reverse preventing means may be formed by a ratchet device or one-way clutch, and the one using a one-way clutch in the form of a ball-type one-way clutch was disclosed in Japanese patent application No. 8-350702 (kokai publication No. 10-181529) filed by the common assignee.
In this ball-type one-way clutch, a plurality of small chambers are defined between an inner race and an outer race each of which gets progressively narrower in a circumferential direction and receives a ball therein. Each ball is urged by a spring toward a narrower part of the chamber.
Typically, the springs consist of compression coil springs. Because the springs and balls are needed as many as the number of the chambers, a large number of components are required, and this complicates the management of component parts. In particular, when the inner race and/or the outer race is integral with other parts of the pretensioner device, and the reversing preventing device cannot be therefore formed as a subassembly, the assembly work tends to be complicated because of the need to install a ball and spring in each of a large number of small chambers.
The present invention was made in view of such problems of the prior art, and its primary object is to provide a seat belt pretensioner device which requires a small number of component parts thereby simplifying the management of component parts and facilitating the assembly work.
According to the present invention, such an object can be accomplished by providing a seat belt pretensioner device, comprising a seat belt buckle which is supported in a moveable manner, a power generator for moving the buckle in a direction to increase a tension of the seat belt, and a reverse preventing device for preventing the reversal of the movement of the buckle, characterized in that: the reverse preventing device consists of a ball-type one-way clutch defining a plurality of chambers between an inner race and an outer race, each of said chambers narrowing in a rotational direction and receiving a ball and a spring urging the ball toward a narrower part of the corresponding chamber; and the springs are formed by bending a plurality of projections integrally formed in a peripheral part of a single disk shaped plate member into a wavy form.
Thereby, the multiplicity of springs can be formed with a single member, and properly positioned simultaneously.